Recent studies from this laboratory have utilized ASL1 murine leukemia cells synchronized by gradient centrifugation to study the cell cycle specific expession of thymus leukemia antigen (TL). Cells treated with anti-TL serum and complement are killed maximally in S phase with little or no killing of cells in G1 or M. Quantitative absorption analysis (inhibition of cytotoxicity) indicated that S phase cells have 3 times as much TL as either G1 or G2 plus M cells. Exponentially growing cells fail to grow in the presence of TL anti-serum (no complement) and in these cells treated with anti-TL the rate of DNA synthesis declines rapidly. The objectives of this proposal are to precisely define the biochemical events involved in inhibition of cell division by TL-anti-TL interaction. Relevant experiments which will be done include 1) determining the pool size, if any, for TL, 2) determining the rate of biosynthesis of TL and were in the cell cycle synthesis occurs, 3) determining the rate of TL degradation and where in the cell cycle degradation occurs, 4) determining how TL-anti-TL interacion effects: (a) the biosynthesis and degradation of TL and the other proteins; (b) DNA rate of synthesis and content per cell and (c) total and specific RNA synthesis.